CSCI Topics: Internet Programming Fall 2008

(1)

CSCI 491-01

Topics: Internet Programming

Fall 2008

CSCI 491

-

01

01 Topics: Internet Programming

Topics: Internet Programming

Fall 2008

Introduction

Derek Leonard Derek Leonard Hendrix College Hendrix College September 3, 2008 September 3, 2008

Original slides copyright

(2)

2

Chapter 1: Introduction

Our goal today:

• Understand course

structure and

terminology

• More depth, detail

later in the course

• Approach:

━ Use the Internet as example

Chapter overview:

• What’s the Internet

• What’s a protocol?

• Network edge

• Network core

• Performance: loss, delay

• Security

• Protocol layers, service

models

(3)

Chapter 1: Roadmap

1.1 What is the Internet?

1.2 Network edge

1.3 Network core

1.4 Delay & loss in packet-switched networks

1.5 Protocol layers, service models

1.6 Networks under attack: security

(4)

4

The Internet: “Nuts and Bolts” View

The Internet:

“

Nuts and Bolts

”

View

• 1) Millions of connected

computing devices:

━

Hosts = end systems

━

Run

network apps

• 2) Communication links:

(5)

5

The Internet: “Nuts and Bolts” View

The Internet:

“

Nuts and Bolts

”

View

• 4) Protocols

control

sending, receiving of msgs

━ E.g., TCP, IP, HTTP, FTP, PPP

• Internet: “network of

networks”

━ Loosely hierarchical

━ Public networks / private intranets

• Internet standards

━ RFC: Request for comments

(6)

6

What’s the Internet: A Service View

What

’

s the Internet: A Service View

• Internet provides a

communication

infrastructure

━ Enables distributed applications:

━ Web, email, games, e-commerce, file sharing

• Communication services:

━ Connectionless/unreliable

(7)

What’s a Protocol?

What

’

s a Protocol?

Human protocols:

• “What’s the time?”

• “I have a question”

• Introductions

… specific msgs sent

… specific actions taken when msgs received, or other events

Network protocols:

• Machines rather than

humans

• All communication activity

in the Internet governed by

protocols

Protocols define format, order

of messages sent and

received among network

(8)

8

What’s a Protocol?

What

’

s a Protocol?

A human protocol and a computer network protocol:

(9)

Chapter 1: Roadmap

1.1 What is the Internet?

1.2 Network edge

1.3 Network core

1.4 Delay & loss in packet-switched networks

1.5 Protocol layers, service models

1.6 Networks under attack: security

(10)

10

A Closer Look at Network Structure:

• Network edge:

━ Applications and hosts

━ 400+ million hosts

━ 20 billion+ web pages

• Network core:

━ Routers

(11)

The Network Edge:

• End systems (hosts):

━ Run application programs

━ E.g., Web, email

━ At “edge of network”

• Client/server model

━ Client host requests, receives service from always-on server

━ Example: web browser/server; email client/server

• Peer-peer model:

━ Minimal (or no) use of dedicated servers

(12)

12

Access Networks and Physical Media

Q: How to connect end

systems to edge router?

• Residential access nets

• Institutional access

networks (school,

company)

(13)

Residential Access: Point to Point Access

• Dialup via modem

━ Up to 56 kb/s direct access to router (often less)

━ Can’t surf and phone at same time: can’t be “always on”

• ADSL: asymmetric digital subscriber line

━ Up to 1 Mbps upstream (today typically < 768 kbps)

━ Up to 8 Mbps downstream (today typically < 3 Mbps)

(14)

14

Residential Access: Cable Modems

• HFC: hybrid fiber coax

━ Asymmetric: up to 30 mb/s downstream, 2 mb/s upstream

• Network

of cable and fiber attaches homes to

ISP router

━ Homes share access to router

(15)

Residential Access: Cable Modems

(16)

16

Cable Network Architecture: Overview

(17)

Cable Network Architecture: Overview

(18)

18

Company Access: Local Area Networks

• Company/univ

local area

network

(LAN) connects

end system to edge router

• Ethernet:

━ Shared or dedicated link connects end system and router

━ 10 mb/s, 100 mb/s, Gigabit Ethernet, 10 GE

(19)

Wireless Access Networks

• Shared wireless access

network connects end system

to router

━ Via base station aka “access point”

• Wireless LANs:

━ 802.11b: 11 mb/s

━ 802.11a: 54 mb/s

• Wide-area wireless access

━ Provided by telco operator

(20)

20

Home Networks

Typical home network components:

• ADSL or cable modem

• Router/firewall/NAT

• Ethernet

• Wireless access point

(21)

Physical Media

• Physical link:

what lies

between transmitter &

receiver

• Guided media:

━ Signals propagate in solid media: copper, fiber

• Unguided media:

━ Signals propagate freely, e.g., radio

Twisted Pair (TP)

(22)

22

Physical Media: Coax, Fiber

Coaxial cable:

• Two concentric copper

conductors

• Bidirectional

• Baseband:

━ Single channel on cable

━ Legacy Ethernet

• Broadband:

━ Multiple channels on cable

━ HFC

Fiber optic cable:

• Glass fiber carrying light

pulses, each pulse a bit

• High-speed operation:

━ high-speed point-to-point transmission (e.g., 200 gb/s)

(23)

Physical Media: Radio

Radio

• Signal carried in

electromagnetic

spectrum

• No physical “wire”

• Bidirectional

• Propagation

environment effects:

━ Reflection ━ Obstruction by objects ━ Interference

Radio link types:

• Terrestrial microwave

━ e.g. up to 45 mb/s channels

• WLAN

━ 2, 11, 54 mb/s

• Wide-area

(e.g., cellular)

━ e.g. 3G: hundreds of kb/s

• Satellite

━ Up to 50 mb/s (or multiple smaller channels)

(24)

24

Chapter 1: Roadmap

1.1 What is the Internet?

1.2 Network edge

1.3 Network core

1.4 Delay & loss in packet-switched networks

1.5 Protocol layers, service models

1.6 Networks under attack: security

(25)

The Network Core

• Mesh of interconnected

routers

• Fundamental question:

how

is data transferred through

the network?

━ Circuit switching: dedicated circuit per call: telephone network

━ Packet-switching: data sent thru net in discrete “chunks”

• Notation reminder

(26)

26

Network Core: Circuit Switching

• End-end resources

reserved for each “call”

━ Link bandwidth, switch

capacity

━ Dedicated resources: no sharing

━ Circuit-like (guaranteed) performance

(27)

Network Core: Circuit Switching

• Network resources

(e.g., bandwidth)

divided into “pieces”

━ Pieces allocated to calls

━ Resource piece idle if not used by owning call

(no sharing)

• Dividing link bandwidth

into “pieces”

━ Frequency division multiplexing (FDM)

━ Time division

(28)

28

Circuit Switching: FDM and TDM

(29)

Numerical Example

• How long does it take to send a file of 640,000 bits

from host A to host B over a circuit-switched

network?

━ All links are 1.536 mb/s

━ Each link uses TDM with 24 slots (1536/24 = 64000)

━ 500 msec to establish end-to-end circuit

(30)

30

Network Core: Packet Switching

Each end-end data stream

divided into packets

━ Packets of users A and B

share network resources

━ Each packet uses full link bandwidth

━ Resources used as needed

Resource contention:

━ Aggregate resource

demand can exceed amount available

━ Congestion: packets queue, wait for link use

• Store and forward

:

━ Packets move one hop at a time

(31)

Packet Switching: Statistical Multiplexing

• Sequence of A’s and B’s packets does not have a

fixed pattern

statistical multiplexing

━

In TDM, each host gets the same slot in a revolving

TDM frame

A

B

C

10 Mb/s Ethernet 1.5 mb/s

D

_E

statistical multiplexing queue of packets waiting for output

(32)

32

Packet Switching: Store-and-Forward

Packet Switching: Store

-

and

-

Forward

• Takes L/R seconds to

transmit (push out)

packet of L bits on to link

of R bps

• Entire packet must

arrive at router before it

can be transmitted on

next link:

store and

(33)

Packet Switching vs. Circuit Switching

• 1 mb/s link

• Each user:

━ 100 kb/s when “active” ━ Active 10% of time

• Circuit-switching:

━ Supports 10 users

• Packet switching:

━ With 35 users, probability that more than 10 users are active is 0.0424%; with 50 users – 0.94%

━ Max 100 users (if perfectly unsynchronized)

Packet switching allows more users to use network!

N users

(34)

34

Packet Switching vs. Circuit Switching

• Great for bursty data

━ Resource sharing

━ Simpler, no call setup

• But suffers from excessive congestion (packet delay

and loss)

━ Protocols needed for reliable data transfer, congestion control

• Q: How to provide circuit-like behavior?

━ Bandwidth guarantees needed for audio/video apps

━ Still an unsolved problem (chapter 7)

(35)

Internet Structure: Network of Networks

• Roughly hierarchical

• In the center:

“tier-1” ISPs (e.g., UUNet, BBN/Genuity,

Sprint, AT&T), national/international coverage

━ Treat each other as equals

━ Form the backbone of the Internet

(36)

36

Tier-1 ISP: XO Communications (2001)

Tier

(37)

Internet Structure: Network of Networks

• “Tier-2” ISPs: smaller (often regional) ISPs

━ Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier 1 ISP

NAP Tier-2 ISP Tier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

(38)

38

Internet Structure: Network of Networks

• “Tier-3” ISPs and local ISPs

━ Last hop (“access”) network (closest to end systems)

Tier 1 ISP

Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP

(39)

Internet Structure: Network of Networks

• A packet passes through many networks!

Tier 1 ISP

(40)

40

Network Taxonomy

Telecommunication networks Circuit-switched networks FDM _TDM Packet-switched networks Networks with VCs Datagram Networks